Nanocarbon/aluminum composite material, process for producing the same, and plating liquid for use in said process

ABSTRACT

[Object] To provide a nanocarbon/aluminum composite material having high strength and electrical conductivity for suitable use in a lead wire, a heat exchanger and an automotive part and a process for producing the nanocarbon/aluminum composite material. 
     [Solution] There is provided a plating liquid for nanocarbon/aluminum composite production, comprising an aluminum halide, nanocarbon and 1,3-dialkylimidazolium halide and/or the like, wherein the molar ratio of the aluminum halide to the 1,3-dialkylimidazolium halide and/or the like is in the range of 20:80 to 80:20 and the 1,3-dialkylimidazolium halide and/or the like has an alkyl group with a carbon number of 1 to 12. There are also provided a nanocarbon/aluminum composite production process comprising forming a plating film on a substrate surface by electrolysis of the plating liquid in a dry, oxygen-free atmosphere with the passage of a direct current etc. under the electrolysis conditions of a bath temperature of 0 to 300° C. and a current density of 0.01 to 50 A/dm 2  and a nanocarbon/aluminum composite material produced by this production process.

TECHNICAL FIELD

The present invention relates to a nanocarbon/aluminum compositematerial, particularly suitable for use in electric conductors such aspower cables and lead wires, heat exchangers such as radiators,condensers and evaporators and automotive parts, a process forproduction of the nanocarbon/aluminum composite material and a platingliquid for use in the nanocarbon/aluminum composite production process.

BACKGROUND ART

In general, power cable and lead wire materials such as aluminum alloysand heat exchanger materials are required to have high electricalconductivity and high thermal conductivity.

From the recent viewpoint of global environmental conservation, there isa growing need for weight and size reductions of power cables, leadwires, heat exchangers and automotive parts. It is thus desired that thematerials of the power cables, lead wires, heat exchangers andautomotive parts have high strength while being shaped in-thinner forms.

The largest number of studies has so far been made on carbon-fiberreinforced aluminum alloys as high-strength light-weight compositematerials. (Refer to Patent Documents 1 and 2.)

Also, attention has recently been given to carbon nanotube (hereinafterreferred to as “CNT”) as carbon fiber. The applicability of CNT is beingexamined in expectation of further performance improvements because ofexcellent CNT properties e.g. toughness, electrical conductivity andthermal conductivity.

Various metals such as copper, nickel and aluminum are used as matricesfor production of CNT composite materials. (Refer to Patent Documents 3and 4.) In particular, it is reported that CNT/aluminum compositematerials increase in strength and attain high thermal conductivity.(Refer to Non-Patent Document 1.)

On the other hand, various aluminum material production processes suchas three-layer electrolysis, fractional crystallization andelectrodeposition are known. Among others, the electrodeposition can becarried out in a single process step and thus regarded as mostattractive. However, the electrodeposition of aluminum from a watersystem is impractical under the influence of competitive hydrogengeneration reaction due to the fact that aluminum has a negativestandard electrode potential of −1.68 V vs. SHE (standard hydrogenelectrode). The electrodeposition of aluminum from an organic solventsystem is feasible, but is difficult to put into industrially practicaluse due to the danger of flashing.

Patent Document 1: Japanese Laid-Open Patent Publication No. 2005-008989Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-048206Patent Document 3: Japanese Laid-Open Patent Publication No. 2004-156074Patent Document 4: Japanese Laid-Open Patent Publication No. 2004-315297Non-Patent Document 1: Journal of Materials Research, T. Kuzamaki etal., 1998, Vol. 13, P. 2445 DISCLOSURE OF THE INVENTION Problems to beSolved by the Invention

Each of the nanocarbon/aluminum composite material production processesof Patent Documents 1-4 and Non-Patent Document 1 includes a complicatedseries of process steps, e.g., placing an aluminum powder and CNT intoan aluminum case, followed by heating at 600° C. for 1.5 hour under areduced pressure of 5.3·10⁻¹ Pa, pressurizing at 100 MPa for 60 minutes,and then, extruding at 10 MPa/min and 600° C. In these productionprocesses, the nanocarbon is added and mixed by stirring into the moltenmetal. There thus arises a problem that it is difficult to disperse thenanocarbon uniformly in the molten metal because of the large differencein specific gravity between the metal and the nanocarbon.

The carbon-fiber/aluminum composite material shows no sign of strengthdeterioration when heated at 500° C. or lower in a non-oxidizingatmosphere. However, there arises a problem in the carbon-fiber/aluminumcomposite material that the interface reaction between the matrix andthe carbon fiber occurs to form aluminum carbide (Al₄C₃) and therebydecrease not only the cross section of the carbon fiber but also thestrength of the carbon fiber due to the occurrence of a notch effect atthe carbide end when the heating retention time becomes higher than orequal to 550° C.

It has also been shown by previous researches that the carbon fiber getsoxidized by heating in the air and faces a serious problem ofdeterioration.

In view of the above prior art problems, the present invention has beenmade to provide a nanocarbon/aluminum composite material having highstrength and electrical conductivity for suitable use in electricconductors such as power cables and lead wires, heat exchangers such asradiators, condensers and evaporators and automotive parts, a processfor production of the nanocarbon/aluminum composite material and aplating liquid for use in the nanocarbon/aluminum composite productionprocess.

Means for Solving the Problems

As a result of extensive researches, the present inventors have produceda technical finding that an room-temperature molten salt (also called“cold molten salt”, “ambient-temperature molten salt” or “ionic liquid”)is expected to be especially useful for various alloy electrodepositionbaths and cell electrolytes in terms of the following advantages(1)-(3).

(1) The room-temperature molten salt allows easy plating of any metal oralloy e.g. aluminum having a negative standard electrode potential.(2) The room-temperature molten salt is usable at room temperature andeasy to handle.(3) The room-temperature molten salt shows non-volatility andnon-flammability and has no danger of flashing.

Based on such a technical finding, the present inventors have proceededwith further researches and found that the above object of the presentinvention can be accomplished by preparing and using a specific platingliquid.

Namely, there is provided a plating liquid for nanocarbon/aluminumcomposite production according to the present invention, comprising analuminum halide, nanocarbon and 1,3-dialkylimidazolium halide and/ormonoalkylpyridinium halide, wherein the molar ratio of the aluminumhalide to the 1,3-dialkylimidazolium halide and/or themonoalkylpyridinium halide is in the range of 20:80 to 80:20; the1,3-dialkylimidazolium halide has an alkyl group with a carbon number of1 to 12; and the monoalkylpyridinium halide has an alkyl group with acarbon number 1 to 12

There is provided a first process for preparing the plating liquid fornanocarbon/aluminum composite production according to the presentinvention, comprising: mixing aluminum halide and nanocarbon together,mixing the mixture of the aluminum halide and the nanocarbon with1,3-dialkylimidazolium halide and/or monoalkylpyridinium halide, andthen, melting the mixture of the aluminum halide, the nanocarbon and the1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide; ormixing nanocarbon with 1,3-dialkylimidazolium halide and/ormonoalkylpyridinium halide, mixing the mixture of the nanocarbon and the1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide withaluminum halide, and then, melting the mixture of the aluminum halide,the nanocarbon and the 1,3-dialkylimidazolium halide and/or themonoalkylpyridinium halide.

There is provided a second process for preparing the plating liquid fornanocarbon/aluminum composite production according to the presentinvention, comprising: mixing aluminum halide and nanocarbon together ormixing nanocarbon with 1,3-dialkylimidazolium halide and/ormonoalkylpyridinium halide, and then, mixing the nanocarbon mixture witha molten salt of aluminum halide and 1,3-dialkylimidazolium halideand/or monoalkylpyridinium halide.

There is also provided a process for producing a nanocarbon/aluminumcomposite material by using the plating liquid for nanocarbon/aluminumcomposite production according to the present invention, comprising:forming a plating film on a substrate surface by electrolysis of theplating liquid in a dry, oxygen-free atmosphere with the passage of adirect current and/or a pulsed current under the electrolysis conditionsof a bath temperature of 0 to 300° C. and a current density of 0.01 to50 A/dm².

There is further provided a nanocarbon/aluminum composite materialproduced by the nanocarbon/aluminum composite production processaccording to the present invention.

Effect of the Invention

It is possible in the present invention to provide a nanocarbon/aluminumcomposite material having high strength and electrical conductivity forsuitable use in electric conductors such power cables and lead wires,heat exchangers such as radiators, condensers and evaporators andautomotive parts and a process for production of the nanocarbon/aluminumcomposite material by the preparation and use of a specific platingliquid.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the plating liquid for nanocarbon/aluminum compositeproduction according to the present invention will be described below indetail. In the following description, all percentages (%) are by massunless otherwise specified.

The plating liquid for nanocarbon/aluminum composite productionaccording to the present invention contains an aluminum halide,nanocarbon and either one or both of 1,3-dialkylimidazolium halide andmonoalkylpyridinium halide, wherein the molar ratio of the aluminumhalide to the 1,3-dialkylimidazolium halide and/or themonoalkylpyridinium halide is in the range of 20:80 to 80:20; the1,3-dialkylimidazolium halide has an alkyl group or groups with a carbonnumber of 1 to 12; and the monoalkylpyridinium halide has an alkyl groupwith a carbon number of 1 to 12 as mentioned above.

In the present invention, it is essential that the molar ratio of thealuminum halide to the 1,3-dialkylimidazolium halide and/or themonoalkylpyridinium halide is in the range of 20:80 to 80:20.

If the above molar ratio is not satisfied, the resulting liquid does notget molten at room temperature and thus cannot be used as the platingliquid. Even when molten at higher temperature, the resulting liquid istoo high in viscosity and not suitable as the plating liquid forproduction of the nanocarbon/aluminum composite material with highstrength and electrical conductivity.

Herein, the 1,3-dialkylimidazolium halide and the monoalkylpyridiniumhalide can be used alone or in combination thereof as long as the abovemole ratio condition is satisfied.

It is also essential in the present invention that the1,3-dialkylimidazolium halide has an alkyl group with a carbon number of1 to 12; and the monoalkylpyridinium halide has an alkyl group with acarbon number of 1 to 12.

If the alkyl group does not have the above carbon number, the resultingliquid does not get molten at room temperature and thus cannot be usedas the plating liquid. Even when molten at higher temperature, theresulting liquid is too high in viscosity and not suitable as theplating liquid for production of the nanocarbon/aluminum compositematerial with high strength and electrical conductivity.

With the above composition, however, the plating liquid is capable ofbeing used to produce the nanocarbon/aluminum composite material withhigh strength and electrical conductivity.

It is preferable in the present invention that the nanocarbon iscontained in an amount of 0.01 to 50 g/L, more preferably 0.01 to 20g/L, with respect to the total volume of the aluminum halide and the1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide.

If the nanocarbon content amount is less than 0.01 g/L, the amount ofnanocarbon particles in aluminum plating is so small that it may becomedifficult for the plating to obtain desired properties. If thenanocarbon content amount exceeds 50 g/L, the concentration ofnanocarbon particles in the electrolytic bath is so high that thenanocarbon particles may get aggregated and precipitated and, at thetime of raising the product from the electrolytic bath upon completionof the electrolysis, adhered excessively to the product.

The respective liquid components will be described in more detail below.

An explanation of the aluminum halide will be first given below.

There is no particular restriction on the aluminum halide as long as thealuminum halide is capable of being used in the above plating liquid forproduction of the nanocarbon/aluminum composite material. For example,aluminum chloride (AlCl₃) is preferably usable. It is particularlypreferable to use anhydrous AlCl₃.

Next, an explanation of the 1,3-dialkylimidazolium halide will be givenbelow.

There is no particular restriction on the 1,3-dialkylimidazolium halideas long as the 1,3-dialkylimidazolium halide has at least one alkylgroup with a carbon number of 1 to 12 and is capable of being used inthe above plating liquid for production of the nanocarbon/aluminumcomposite material. It is preferable that the 1,3-dialkylimidazoliumhalide has one alkyl group with a carbon number of 1 to 5, morepreferably two alkyl groups with a carbon number of 1 to 5. Morespecifically, 1-ethyl-3-methylimidazolium chloride (hereinafter referredto as “EMIC”) is preferably usable. These two alkyl groups may be thesame or different.

An explanation of the monoalkylpyridinium halide will be given below.

There is no particular restriction on the monoalkylpyridinium halide aslong as the monoalkylpyridinium halide has an alkyl group with a carbonnumber of 1 to 12 and is capable of being used in the above platingliquid for production of the nanocarbon/aluminum composite material. Itis preferable that the monoalkylpyridinium halide has one alkyl groupwith a carbon number of 1 to 5. More specifically, 1-butylpyridiniumhalide (hereinafter referred to as “BPC”) is preferably usable.

In terms of the physical properties, notably electrical conductivity,viscosity and melting point, of the plating liquid, it is preferable touse the EMIC having a low melting point of about 84° C.

An explanation of the nanocarbon will be given below.

There is no particular restriction on the nanocarbon. As the nanocarbon,there can be used carbon nanotube, carbon nanofiber, carbon nanohom,fullerene, carbon black, acetylene black, ketjen black or any mixturethereof.

It is preferable in the present invention to use, as one kind ofnanocarbon, carbon nanotube with a diameter of 1 to 100 nm, a length of1 to 100 μm and an aspect ratio of 10 to 100.

If the carbon nanotube diameter is smaller than 1 nm, it is likely thatthe carbon nanotube will get aggregated and precipitated so that it isdifficult to incorporate a sufficient amount of carbon nanotube inaluminum plating. If the carbon nanotube diameter exceeds 100 nm, it isalso likely that the carbon nanotube will get precipitated so that it isdifficult to incorporate a sufficient amount of carbon nanotube inaluminum plating. If the carbon nanotube length is less than 1 μm, it islikely that the carbon nanotube will get aggregated and precipitated sothat it is difficult to incorporate a sufficient amount of carbonnanotube in aluminum plating as in the case where the carbon nanotubediameter is smaller than 1 nm. If the carbon nanotube length exceeds 100μm, it is also likely that the carbon nanotube will get precipitated sothat it is difficult to incorporate a sufficient amount of carbonnanotube in aluminum plating as in the case where the carbon nanotubediameter exceeds 100 nm.

Herein, the carbon nanotube may have either a single-wall structure, amulti-wall structure or any composite structure thereof.

Next, the preparation of the plating liquid for nanocarbon/aluminumcomposite production according to the present invention will beexplained below.

A first process of preparing the plating liquid for nanocarbon/aluminumcomposite production according to the present invention includes mixingan aluminum halide and nanocarbon together, mixing the resulting mixturewith either one or both of 1,3-dialkylimidazolium halide andmonoalkylpyridinium halide and melting the mixture, or mixing ananocarbon with either one or both of 1,3-dialkylimidazolium halide andmonoalkylpyridinium halide, mixing the resulting mixture with analuminum halide and melting the mixture.

A second process of preparing the plating liquid for nanocarbon/aluminumcomposite production according to the present invention includes mixingan aluminum halide and nanocarbon together, or mixing nanocarbon witheither one or both of 1,3-dialkylimidazolium halide andmonoalkylpyridinium halide, and then, mixing the resulting mixture witha molten salt of the aluminum halide and either one or both of1,3-dialkylimidazolium halide and monoalkylpyridinium halide.

In the first and second preparation processes, both of the1,3-dialkylimidazolium halide and the monoalkylpyridinium halide havealkyl groups with a carbon number of 1 to 12, which may be the same ordifferent.

There are no particular restrictions on the aluminum halide and thenanocarbon. Any of the above-mentioned aluminum halide and nanocarbonmaterials are usable.

The plating liquid for nanocarbon/aluminum composite productionaccording to the present invention is not limited to those prepared bythe above first and second preparation processes and can be prepared byany process as long as the plating liquid has a specific composition ofaluminum halide, nanocarbon and either one or both of1,3-dialkylimidazolium halide and monoalkylpyridinium halide. In thecase of preparing the plating liquid for nanocarbon/aluminum compositeproduction by the first preparation process, the nanocarbon is mixed inadvance with the salt. This makes the nanocarbon unlikely to getaggregated and thus desirably leads to a uniform dispersion of thenanocarbon in the plating liquid. In the case of preparing the platingliquid for nanocarbon/aluminum composite production by the secondpreparation process, the nanocarbon mixture is directly added into themolten salt of the aluminum halide and the 1,3-dialkylimidazolium halideand/or the monoalkylpyridinium halide. This promotes a desirably moreuniform dispersion of the nanocarbon in the plating liquid.

By way of more specific example, the plating liquid can be prepared bye.g. mixing AlCl₃ as one kind of aluminum halide and EMIC as one kind of1,3-dialkylimidazolium halide at a given molar ratio to obtain aroom-temperature molten salt as a base, followed by adding thereto CNTas one kind of nanocarbon appropriately.

For ease of handling, it is preferable to disperse the CNT into AlCl₃ orEMIC before adding the CNT to the molten salt.

When the room-temperature molten salt is not in a completely moltenstate, it is preferable to melt the salt completely by heating.

It is further preferable to immerse an Al wire in the completely moltensalt before adding the CNT to the molten salt in order to removeimpurities from the AlCl₃-EMIC room-temperature molten salt.

There is no particular restriction on the technique for dispersing theCNT in the AlCl₃-EMIC room-temperature molten salt. For example,ultrasonic irradiation or stirring can be used.

The production of the nanocarbon/aluminum composite material will benext explained below.

A process for producing the nanocarbon/aluminum composite material byusing the plating liquid for nanocarbon/aluminum composite productionaccording to the present invention includes forming a plating film on asubstrate surface by electrolysis of the plating liquid in a dry,oxygen-free atmosphere with the passage of either a direct current, apulsed current or an appropriate combination thereof under theelectrolysis conditions of a bath temperature of 0 to 300° C. and acurrent density of 0.01 to 50 A/dm².

If the bath temperature is lower than 0° C., the plating liquid getssolidified. If the bath temperature exceeds 300° C., the plating liquidgets decomposed by heat. In either case, it is difficult to accomplishthe electrolysis.

If the current density is less than 0.01 A/dm², the electrolysis timebecomes too long for practical use. If the current density exceeds 50A/dm², the plating liquid reaches a decomposition voltage level so thatit is difficult to accomplish the plating.

Herein, the “dry, oxygen-free atmosphere” means an atmosphere with amoisture content of 2 ppm or lower and an oxygen content of 1 ppm orlower in the present invention. An argon (Ar) or nitrogen (N₂)atmosphere is generally usable as the dry, oxygen-free atmosphere.

By the above process, it is possible to produce the nanocarbon/aluminumcomposite material (plating film) with high strength and electricalconductivity on the substrate surface.

It is also possible by means of electroplating in the above process toform the plating film of the nanocarbon/aluminum composite materialeasily in a single process step. Further, the plating film of thenanocarbon/aluminum composite material can be formed into a desiredshape.

There is no particular restriction on the electrolytic technique in theproduction of the nanocarbon/aluminum composite material. For example,the electrolysis can be accomplished by using any known two-electrodecell.

One example of the electrolysis is to apply a voltage to the platingliquid, in which the CNT is dispersed in the AlCl₃-EMIC room-temperaturemolten salt, with a cathode and an anode immersed in the plating liquidand connected to a direct-current power source to feed a constantcurrent, a pulsed current or a combination thereof between these twoelectrodes.

The intensity of the applied voltage may be changed at each period.

The electrolysis may be done intermittently for about 0.1 to 600seconds.

The electrolysis may be done by repeated cycles of voltage applicationand stop as necessary at intervals of about 0.1 to 1 second.

The plating amount of the nanocarbon/aluminum composite material can becontrolled by adjusting the nanocarbon dispersion amount, the currentdensity, the electrolysis time and the like as appropriate.

For example, the plating amount of the nanocarbon/aluminum compositematerial can be increased by increasing the nanocarbon dispersionamount, raising the electrolysis voltage to increase the currentdensity, increasing the electrolysis time or any combination thereof.

In the case of continuous production of the nanocarbon/aluminumcomposite material, it is desirable to replenish the nanocarbon and theAlCl₃-EMIC room-temperature molten salt sequentially so as to complementa decrease in the nanocarbon dispersion amount.

There is no particular restriction on the material and form of thecathode (negative electrode). The cathode can be an electric conductorof any material and form as long as it is chemically andelectrochemically stable toward the plating liquid.

As the cathode material, there can be used e.g. copper, brass, nickel,stainless, tungsten, molybdenum and the like. Copper and brass arepreferred in terms of the electrochemical stability, drawability andcost efficiency, but are not limited thereto.

As the cathode form, the surface configuration, thickness and size arenot particularly restricted. The cathode can be a porous metal substrateof foil form, plate form, spiral wire form, foam form, nonwoven form,mesh form, felt form or expanded form. Among others, foil form and plateform are preferred.

By the above electrolystic technique, the plating film is formed tocover a surface of the cathode as the substrate.

As the anode (positive electrode), any known conductive substrate can beused with no particular restriction. The anode material can bepreferably selected from platinum and graphite that are chemically andelectrochemically stable toward the plating liquid, and aluminum thatdoes not cause contamination of the plating liquid by dissolution.

There is no particular restriction on the form of the anode. The anodecan be of e.g. plate form or spiral form.

Next, the nanocarbon/aluminum composite material according to thepresent invention will be explained below.

In the present invention, the nanocarbon/aluminum composite material isproduced by the above nanocarbon/aluminum composite production process.

The thus-produced nanocarbon/aluminum composite material is capable ofnot only attaining high electrical and thermal conductivity but alsobeing provided in thinner form for weight and size reduction and thus issuitable as a high-strength lightweight composite material for use inpower cables, lead wires, heat exchangers such as radiators, condensersand evaporators, automotive parts and the like.

For example, the plating film of the nanocarbon/aluminum compositematerial can be formed by the above electrolystic technique.

In the present invention, the nanocarbon content of thenanocarbon/aluminum composite material is preferably in the range of 0.1to 50%, more preferably 0.1 to 20%.

If the nanocarbon content is less than 0.1%, the material cannot obtaindesired properties with almost none of nanocarbon characteristicfeatures reflected therein. If the nanocarbon content exceeds 50%, thealuminum content is too low to function as a matrix for establishing abonding between the nanocarbon particles so that thenanocarbon-to-nanocarbon bonding may become weakened to cause a suddendeterioration of material strength.

EXAMPLES

The present invention will be described in more detail with reference tothe following examples. It should be however noted that the followingexamples are only illustrative and not intended to limit the inventionthereto.

Example 1

First, AlCl₃ and EMIC were weighed out at a molar ratio of 66.7:33.3 andmixed together with stirring. The resulting mixture was completelymelted and purified by substitution through the immersion of Al wire inthe mixture for 1 week or more.

A plating liquid for MWCNT/aluminum composite production was prepared byadding 0.1 to 30.0 g/L of multi-wall carbon nanotube (MWCNT with a tubediameter of 1.2 to 2.0 nm and a tube length of 2 to 5 μm) into the abovemixture.

A NWCNT/aluminum composite material was then produced by constantcurrent electrolysis of the plating liquid with sufficient stirring.

Herein, the preparation and electrolysis of the plating liquid werecarried out in a dry nitrogen atmosphere. In the constant currentelectrolysis, a two-electrode cell with a cathode of Cu plate (99.96%)and an anode of Al plate (99.99%) was used. The cathode had beenpretreated by grinding with an emery paper (No. 2000), electrolyticdegreasing with 10% aqueous solution of sodium orthosilicate and thenacid treatment with 10 vol % HCl. The electrolysis conditions were setto a bath temperature of 30° C., a current density of 5, 10, 20, 30mA/cm² and an electrolysis charge amount of 50 C/cm².

A surface state of the NWCNT/aluminum composite material was monitoredby means of a scanning electron microscope (SEM “JSM-6500F” availablefrom JEOL Ltd.) so as to observe the incorporation of NWCNT into the Aldeposit in a practical manner. The observation showed that the NWCNT wasfirst adsorbed onto deposit surfaces, then captured by initial Aldeposit nucleus (about 1 to 100,000 atoms), totally incorporated intothe grown Al deposit nucleus and then almost completely embedded in theAl deposit. It has been found out by the observation that the NWCNT waseutectic with Al and present in monodisperse form.

Further, the MWCNT content of the MWCNT/aluminum composite material wasdetermined to be 0.1 to 20% by means of a total organic carbon meter(“TOC-5000A” available from SHIMADZU Corporation).

The relationship between the MNCNT addition amount of the plating liquidand the Vickers hardness of the composite material was analyzed asfollows. (Refer to FIG. 1.) The analysis was made semiquantitatively onthe assumptions that an increase in the MWCNT eutectic amount couldallow an increase in the composite material hardness and that thehardness of an Al plating film with an MWCNT addition amount of 0 g/Lwas adopted as a comparative example. In the present example, thehardness of the Al plating film was 50 Hv when the current density wasset to any of 50, 10, 20 and 30 mA/cm². As shown in FIG. 1, the hardnessof the composite material became higher than that of the Al plating filmat each current density as the MWCNT addition amount of the plating bathincreased. In view of the fact that a metal generally increases inhardness when nanoparticles exist in the metal, the eutectic of theMWCNT was supported by the increased hardness of the composite materialin the present example. Herein, a Vickers hardness tester (“HM-124”available from AKASHI Co. Ltd.) was used in the hardness measurement.

The specific resistance of the composite material was further determinedby four-terminal measurement according to JIS C 2525 and found to belower than that of the Al plating film.

Based on the above results, analyses were also made on other kinds ofnanocarbon particles. The same effect was obtained by the use of any ofsingle-wall carbon nanotube, carbon nanofiber, carbon nanohom,fullerene, carbon black, acetylene black and ketjen black.

The usability of the nanocarbon/aluminum composite material, compositeproduction method and plating liquid according to the present inventionhave thus been proved as above.

Example 2

A predetermined amount of EMIC and MWCNT (with a tube diameter of 1.2 to2.0 nm and a tube length of 2 to 5 μm) was mixed together, followed byadding AlCl₃ and melting the resulting mixture to yield a plating liquidfor MWCNT/aluminum composite production. The molar ratio of AlCl₃ andEMIC in the plating liquid was set to 66.7:33.3. The MWCNT additionamount was set to 0.1 to 30.0 g/L.

A NWCNT/aluminum composite material was then produced by constantcurrent electrolysis of the plating liquid with sufficient stirring asis the case with Example 1.

The preparation and electrolysis of the plating liquid were hereincarried out in a dry nitrogen atmosphere. Further, the two-electrodeelectrolysis cell, the cathode pretreatment process and the electrolysisconditions were the same as in Example 1.

A surface state of the NWCNT/aluminum composite material was observed bymeans of SEM. It has been found out by the observation that the NWCNTwas eutectic with Al and present in monodisperse form as is the casewith Example 1.

Further, the MWCNT content of the MWCNT/aluminum composite material wasdetermined to be 0.1 to 20% by means of a total organic carbon meter(“TOC-5000A” available from SHIMADZU Corporation).

The relationship between the MNCNT addition amount of the plating liquidand the Vickers hardness of the composite material was analyzed asfollows. (Refer to FIG. 2.) As is the case with Example 1, the analysiswas made on the assumption that the hardness of an Al plating film withan MWCNT addition amount of 0 g/L was adopted as a comparative example.The hardness of the composite material became higher than that of the Alplating film at each current density as the MWCNT addition amount of theplating bath increased As shown in FIG. 2. In view of the fact that ametal generally increases in hardness when nanoparticles exist in themetal, the eutectic of the MWCNT was supported by the increased hardnessof the composite material in the present example. Herein, a Vickershardness tester (“HM-124” available from AKASHI Co. Ltd.) was used inthe hardness measurement.

The specific resistance of the composite material was further determinedby four-terminal measurement and found to be lower than that of the Alplating film.

Based on the above results, analyses were also made on other kinds ofnanocarbon particles. The same effect was obtained by the use of any ofsingle-wall carbon nanotube, carbon nanofiber, carbon nanohorn,fullerene, carbon black, acetylene black and ketjen black.

The usability of the nanocarbon/aluminum composite material, compositeproduction method and plating liquid according to the present inventionhave thus been proved as above.

Example 3

A predetermined amount of EMIC and MWCNT (with a tube diameter of 1.2 to2.0 nm and a tube length of 2 to 5 μm) was mixed together and added toan AlCl₃-EMIC molten salt to yield a plating liquid for MWCNT/aluminumcomposite production. The molar ratio of AlCl₃ and EMIC in the platingliquid was set to 66.7:33.3. The MWCNT addition amount was set to 0.1 to30.0 g/L.

A NWCNT/aluminum composite material was then produced by constantcurrent electrolysis of the plating liquid with sufficient stirring asis the case with Example 1.

The preparation and electrolysis of the plating liquid were hereincarried out in a dry nitrogen atmosphere. Further, the two-electrodeelectrolysis cell, the cathode pretreatment process and the electrolysisconditions were the same as in Example 1.

A surface state of the NWCNT/aluminum composite material was observed bymeans of SEM. It has been found out by the observation that the NWCNTwas eutectic with Al and present in monodisperse form as is the casewith Example 1.

The MWCNT content of the MWCNT/aluminum composite material wasdetermined to be 0.1 to 20% by means of a total organic carbon meter(“TOC-5000A” available from SHIMADZU Corporation).

The relationship between the MNCNT addition amount of the plating liquidand the Vickers hardness of the composite material was analyzed asfollows. (Refer to FIG. 3.) As is the case with Example 1, the analysiswas made on the assumption that the hardness of an Al plating film withan MWCNT addition amount of 0 g/L was adopted as a comparative example.The hardness of the composite material became higher than that of the Alplating film at each current density as the MWCNT addition amount of theplating bath increased As shown in FIG. 3. In view of the fact that ametal generally increases in hardness when nanoparticles exist in themetal, the eutectic of the MWCNT was supported by the increased hardnessof the composite material in the present example. Herein, a Vickershardness tester (“HM-124” available from AKASHI Co. Ltd.) was used inthe hardness measurement.

The specific resistance of the composite material was further determinedby four-terminal measurement and found to be lower than that of the Alplating film.

Based on the above results, analyses were also made on other kinds ofnanocarbon particles. The same effect was obtained by the use of any ofsingle-wall carbon nanotube, carbon nanofiber, carbon nanohom,fullerene, carbon black, acetylene black and ketjen black.

The usability of the nanocarbon/aluminum composite material, compositeproduction method and plating liquid according to the present inventionhave thus been proved as above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a relationship between NWCNT addition amountand material hardness in Example 1 and Comparative Example.

FIG. 2 is a graph showing a relationship between NWCNT addition amountand material hardness in Example 2 and Comparative Example.

FIG. 3 is a graph showing a relationship between NWCNT addition amountand material hardness in Example 3 and Comparative Example.

1. A plating liquid for nanocarbon/aluminum composite production,comprising an aluminum halide, nanocarbon and 1,3-dialkylimidazoliumhalide and/or monoalkylpyridinium halide, wherein the molar ratio of thealuminum halide to the 1,3-dialkylimidazolium halide and/or themonoalkylpyridinium halide is in the range of 20:80 to 80:20; the1,3-dialkylimidazolium halide has an alkyl group with a carbon number of1 to 12; and the monoalkylpyridinium halide has an alkyl group with acarbon number of 1 to
 12. 2. The plating liquid for nanocarbon/aluminumcomposite production according to claim 1, wherein the nanocarbon iscontained in an amount of 0.01 to 50 g/L with respect to the totalvolume of the aluminum halide and the 1,3-dialkylimidazolium halideand/or the monoalkylpyridinium halide.
 3. The plating liquid fornanocarbon/aluminum composite production according to claim 1, whereinthe nanocarbon is at least one selected from the group consisting ofcarbon nanotube, carbon nanofiber, carbon nanohom, fullerene, carbonblack, acetylene black and ketjen black.
 4. The plating liquid fornanocarbon/aluminum composite production according to claim 3, whereinthe nanocarbon tube has a diameter of 1 to 100 μm, a length of 1 to 100μm and an aspect ratio of 10 to
 100. 5. A process for preparing theplating liquid for nanocarbon/aluminum composite production according toclaim 1, comprising: mixing aluminum halide and nanocarbon together,mixing the mixture of the aluminum halide and the nanocarbon with1,3-dialkylimidazolium halide and/or monoalkylpyridinium halide, andthen, melting the mixture of the aluminum halide, the nanocarbon and the1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide; ormixing nanocarbon with 1,3-dialkylimidazolium halide and/ormonoalkylpyridinium halide, mixing the mixture of the nanocarbon and the1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide withaluminum halide, and then, melting the mixture of the aluminum halide,the nanocarbon and the 1,3-dialkylimidazolium halide and/or themonoalkylpyridinium halide.
 6. A process for preparing the platingliquid for nanocarbon/aluminum composite production according to claim1, comprising: mixing aluminum halide and nanocarbon together or mixingnanocarbon with 1,3-dialkylimidazolium halide and/or monoalkylpyridiniumhalide, and then, mixing the nanocarbon mixture with a molten salt ofaluminum halide and 1,3-dialkylimidazolium halide and/ormonoalkylpyridinium halide.
 7. A process for producing ananocarbon/aluminum composite material by using the plating liquid fornanocarbon/aluminum composite production according to claim 1,comprising: forming a plating film on a substrate surface byelectrolysis of the plating liquid in a dry, oxygen-free atmosphere withthe passage of a direct current and/or a pulsed current under theelectrolysis conditions of a bath temperature of 0 to 300° C. and acurrent density of 0.01 to 50 A/dm².
 8. A nanocarbon/aluminum compositematerial produced by the nanocarbon/aluminum composite materialproduction process according to claim
 7. 9. The nanocarbon/aluminumcomposite material according to claim 8, wherein the nanocarbon contentof the nanocarbon/aluminum composite material is in the range of 0.1 to50%.